1. Field of the Invention
The present invention relates to a method and a device for the debouncing of light-characteristic changes (e.g., streetlights, headlights of other vehicles), which are ascertained from image data of a camera for a vehicle, light-characteristic changes being identified in a continuous image sequence and a distance in time being determined between the light-characteristic changes, a spatial distance between the light-characteristic changes being determined with reference to the speed of the vehicle and from the distance in time between the light-characteristic changes, and the debouncing being based on the spatial distance, according to the species defined in the independent claims.
2. Description of Related Art
Systems which actively control the lighting of a vehicle (headlights) have been available on the market for some time. The aim of this measure is first of all, to offer to the driver an optimal view of the roadway in front of him/her, i.e., the relevant traffic situation, and secondly (of lower priority), to avoid obstructing the view of other road users or persons (pedestrians, bicyclists) or objects (building) to the greatest extent possible. Special systems which prevent the blinding of oncoming vehicles and automatically switch between high beam and low beam have been known for a longer time.
Systems which adapt the light-distribution pattern specially to the instantaneous driving situation, or to the area being driven through, have been known for a shorter time. Active headlight leveling control or swiveling headlights could be named as example for the first, and special light-distribution patterns such as freeway light or urban-light mode could be named for the second. The light-distribution pattern of the urban-light mode manifests itself through a large, wide illumination characteristic which makes it possible to see intersections better and to illuminate the sidewalks, since increasingly road users are stopping especially in municipal (that is, populated) areas. Such a headlight, which permits a variable light characteristic owing to suitable control, is described in published international patent application document WO 2006/116960 A1, for example.
In order to be able to control such headlights correctly and automatically, the vehicle must have means capable of determining the instantaneous driving situation or the whereabouts of the vehicle. For various purposes, there are already such systems which detect objects at night with the aid of a camera (e.g., dual purpose camera (DPC) or multi-purpose camera (MPC)).
The U.S. Pat. No. 6,861,809 B2 describes detecting whether a vehicle is in an urban area based on the light intensity that is measured by a special intensity sensor. If the intensity of the ambient light is high, it is assumed that the vehicle is in a lighted area and thus in the city, and activation of the urban-light mode is recommended. In particular, these ambient-light sensors detect whether the light has a non-discernable alternating-voltage characteristic attributable to the power-line frequency. This method proves unsuccessful when LED streetlights are used, since they have their own clocking or no clocking at all.
Moreover, it is known to switch a certain light-distribution pattern on or off with the aid of a speed threshold, that is, when the vehicle exceeds or falls below a specific speed. In particular, a possible urban-light mode is deactivated when a specific speed is exceeded.
In column 12, lines 17-21 of U.S. Pat. No. 6,861,809, the use of an imaging sensor is mentioned briefly, by which streetlights are identified and the urban-light mode is activated when a specific number of streetlights are detected within a certain time. This teaching does not consider whether a vehicle travels a great distance within this time span, and therefore has already driven some distance in the city before the urban-light mode is activated. The consideration of the vehicle speed mentioned at this point relates to the previously described speed threshold, in response to the exceeding of which, the urban-light mode is generally switched off, and the standard light is switched on.
For example, known light-distribution patterns have the self-explanatory designations of freeway light, bad-weather light or urban-light mode. Here, in most cases, standard light is understood to be low beam or high beam.
A street-lighting unit is understood to be a light source which illuminates the road and/or is able to be perceived by the camera of the vehicle. For the present invention, it must fulfill the purpose to be characteristic for a lighted area. Typically, it means streetlights or lamps, especially those which illuminate a street or a street lined with houses over a greater length, and not only at certain points for hazardous situations. This rules out lights which are not used primarily for this purpose, especially those which are mobile, such as headlights of other vehicles. Light sources (active or passive) may also be suitable for this, such as traffic lights, other signal lights or reflections from traffic signs. For example, a frequent appearance of traffic lights indicates a lighted and built-up area, as well.
A light characteristic change is the modification of an instantaneous light situation (light variation), that is, a change in the strength, distribution, color, frequency, modulation (e.g., AC power supply voltage) of the light incoming from the surroundings and falling on the vehicle, i.e., the detecting sensor (light sensor, camera). The characteristic may be determined by certain light variations, for example, by the change in the incidence of light when passing an oncoming vehicle, or the light change already described, when passing stationary objects such as streetlights, for example. A characteristic may also be shaped by more than one light change, for example, a certain number of light changes within a specific time, or a sequence of different light colors. One possible characteristic may be a light-dark change such as upon exiting a lighted tunnel; another characteristic may be a dark-light-dark change, such as when passing by a streetlight. Such a passing may also be interpreted as 2 characteristic changes: dark-light and following that, light-dark.
The term “stationary state” of objects is understood to be their state of being fixed in place, that is, the stationary state of the object is given when the object is a stationary object.
In the present case, the term debouncing is used in such a way that, to be correct, it would have to mean hysteresis. The Wikipedia encyclopedia defines this as follows: “Hysteresis characterizes a system whose output variable is not solely a function of the type of input variable, but also of the history which the input variable had. The system thereby demonstrates path dependency.”
Light characteristic changes are processed as a function of the occurrence of previous light characteristic changes and states of a system influenced by them (e.g., present headlight adjustment).
Traditionally, a debouncing is known in the case of a switch which can generate several unwanted bounce pulses during the closing or opening operation. For example, a Schmitt trigger, which has a hysteresis functionality, may provide a corrective for this, in that after a last pulse, it waits a defined time to see whether a further pulse will occur. If not, the switching operation is regarded as complete and ended and is output/signaled.
Another type of debouncing may be the waiting for a certain number of events before an action is carried out and the debouncing is ended.
In like manner, a certain time may be waited after a light characteristic change, in order, for example, to detect a further (or n further) streetlight(s), or to output a signal (e.g., to activate a special light-distribution pattern of a headlight). This “waiting according to the time” is known from the related art; therefore, the present invention deals with the waiting and debouncing according to the distance or the speed, as explained below.
The terms area and region are to be used synonymously in the present case; in particular, a municipal area denotes an urban area, synonymous with an inner-city or populated area of an urban neighborhood, however, not restricted to city limits or municipality boundaries, but rather to communities, or populated or busy areas in general.